It sounds to me as if the separation of the plugins is the main issue here.
So, would the following option be a viable solution?
What if you could purchase a special version of Maxwell Studio (i.e. a bit more money than the regular version of Studio) that comes with all of the previous plugins including the discontinued plugins?
The only caveat here would be that these plugins would merely act as "dynamic links" that open up Maxwell Studio allowing you to render your model and, of course, save the Maxwell file. You would have the full version of Studio but there would be no integration of the plugins with your 3d Software whatsoever (you would have to separately purchase the fully integrated version of a given plugin for that).
Because it's a "dynamic link" to your model it will update as you make changes to your model. Any materials that you apply in Studio will, of course, update as well.
Does this seem like a reasonable solution? (Please know that I'm merely a user, a creative solutions type of guy
, and I have no affiliation with the company nor do I know anything about its business decisions.)